Piezoelectric materials are generally ABO3 perovskite-type metal oxides such as lead zirconate titanate (hereinafter referred to as “PZT”). PZT contains lead as an A site element, and therefore its influence on environment is viewed as a problem. Accordingly, there is a demand for a piezoelectric ceramic including a lead-free perovskite-type metal oxide.
PTL 1 discloses that the piezoelectric constant is increased by adding cobalt to a piezoelectric ceramic, a solid solution of sodium niobate and barium titanate (hereinafter referred to as “NN-BT”). A composition having a low piezoelectric constant d31 of 12 pC/N has a mechanical quality factor Qm of 1020. However, it is described that a composition having a piezoelectric constant d31 of 54 to 56 pC/N (an NN-BT ceramic sample having a barium titanate concentration of 9% to 11%) has a decreased mechanical quality factor Qm of 250 to 430. It is also disclosed that some of the piezoelectric materials in PTL 1 have deteriorated insulation resistance values of 106Ω or less and are therefore hardly polarized.